@Thalassicus:
I've been tracking down some curious side effects that I *believe* are being caused by this mod component. It concerns how the changes affect the yields of city center tiles. I'm not quite 100% sure it's coming from this mod, because it's hard to test it definitively. Here's what I've found so far:
Something increases the yields of all central city tiles from 2 Food to 3 Food during the game. It doesn't happen in vanilla. I'm pretty sure I've linked this to the change to Fertilizer tech which now gives added food yield to all farms, regardless of freshwater status. This in itself is not a bad or surprising thing - the assumption is that city center tiles are being farmed, I guess. What's curious is that without the mod, river cities do not get a +1 Food bonus post-Fertilizer as you might expect, despite having Freshwater access. Still, no big deal, although perhaps this could be documented in the readme.
Where it gets stranger: With the mod, all central city tiles get the +1 Food, EXCEPT the capital city! That's right, for some weird reason, the capital is treated differently that all the other cities. It isn't being "farmed". This "bug" (?) is what originally led me into this weird rabbit hole in the first place. I was trying to double check the mod's effect on maritime food bonuses, and noticed it wasn't adding up at the capital - it was off by 1 from what the tooltip seemed to imply. That's when I discovered the capital falls behind by 1 food somehow. Usually people wouldn't notice because the larger maritime bonus tends to obscure this small bonus.
I've tried removing the fertilizer code in the .xml, but this doesn't change the city center yields upon loading. I also tried adding the fertilizer food bonus into both "freshwater" and "non-freshwater" yield tables, with no effect. I assume it's because tech-triggered yield changes are only processed when the tech is discovered, as you once mentioned when we were discussing reloads with regards to the Butcher. I don't have a save handy that's just before discovering Fertilizer to test this with properly.
While testing the curious food bonus, I noticed there is also an unexplained +1 Production bonus being added to the center tile of all cities at some point during the game. Again, this doesn't happen in vanilla. In this case there is no difference between the capital and other cities. I'm not at all sure when & why it's happening, but I'm guessing it's from a tech being researched. I do not have the Republic Social Policy researched at any point during my test game (it gives +1 Prod to all cities). There are no wonders or other policies that account for this. The bonus is not there after Engineering, and is there after Steam Power. If I had to guess I'd think it's this mod's added Lumber Mill bonus that's triggering it for some reason. In any case it's something that happens in the Renaissance or early Industrial era. I would have thought it would be Mining tech, but it doesn't happen that early. Both this & the food bonus happen without Railroad having been researched.
I'm just curious if anyone can verify or explain my findings. It's not very big deal balance-wise, obviously. If it is this mod, I don't imagine anything reasonable can/will be done about this, except perhaps some additional documentation to explain the phenomenon.